During next year we intend to continue to expand our program in the determination of the thermodynamic properties of the siderophores and model compounds. We hope to characterize by x-ray crystallography the structures of several model siderophores and perhaps one or two actual siderophore complexes. We are particularly anxious to study enterobactin and have obtained crystals of almost a suitable size. We plan to carry out transport experiments with rhodotorulic acid/or enterobactin using metal-substituted kinetically-inert isomers.